cmd/internal/obj/loong64: save LR after decrementing SP

Refer to CL 413428 and 412474, for loong64, like mips, s390x and riscv, there
is no single instruction that saves the LR and decrements the SP, so we also
need to insert an instruction to save the LR after decrementing the SP.

Fixes golang#56623.
Updates golang#53374.

Change-Id: I3de040792f0a041d3d2a98ea89c23a2dd2f4ad10
Reviewed-on: https://go-review.googlesource.com/c/go/+/416154
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
Auto-Submit: Cherry Mui <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>
Reviewed-by: WANG Xuerui <[email protected]>
Reviewed-by: xiaodong liu <[email protected]>
Run-TryBot: Cherry Mui <[email protected]>
Reviewed-by: Meidan Li <[email protected]>
(cherry picked from commit 3ed8a1e)

Author: abner-chenc

src/cmd/internal/obj/loong64/obj.go

@@ -260,6 +260,20 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 				q.Spadj = +autosize
 
 				q = c.ctxt.EndUnsafePoint(q, c.newprog, -1)
+
+				// On Linux, in a cgo binary we may get a SIGSETXID signal early on
+				// before the signal stack is set, as glibc doesn't allow us to block
+				// SIGSETXID. So a signal may land on the current stack and clobber
+				// the content below the SP. We store the LR again after the SP is
+				// decremented.
+				q = obj.Appendp(q, newprog)
+				q.As = mov
+				q.Pos = p.Pos
+				q.From.Type = obj.TYPE_REG
+				q.From.Reg = REGLINK
+				q.To.Type = obj.TYPE_MEM
+				q.To.Offset = 0
+				q.To.Reg = REGSP
 			}
 
 			if c.cursym.Func().Text.From.Sym.Wrapper() && c.cursym.Func().Text.Mark&LEAF == 0 {